1. Field of the Invention
The present invention relates to a method for dewatering suspensions, in particular communal sewage sludge in a cylindrical filter drum which can be rotated about an axis, having discharge means at the opposite end from the feeding inlet and, if desired, in its interior baffles, for example, ring-shaped wier-like obstructions.
2. Prior Art
Such filter drums with a horizontal axis are well known, the peripheral speed of which is the same over the entire length. The filter drum is required to offer a continually large fresh filter surface to the usually very watery suspension; for this reason a relatively high peripheral speed at a certain diameter is employed. With progressive dewatering which proceeds along with the transportation of the suspension to be dewatered in the direction towards the outlet end of the filter drum, the volume of the suspension decreases markedly, its consistency increases and a sludge cake, which rolls around in the lower region of the filter drum, is formed. This sludge cake releases relatively little water and therefore only a small fresh filter surface needs to be made available for it. With cylindrical filter drums, however, the same high peripheral speed of the inlet zone is also experienced at the outlet zone. This means that the sludge cake is subjected to high mechanical stresses, which leads to a breaking up of the desired, very sensitive flakes.